The purpose of this study was to investigate the effect of high-pressure carbon dioxide (HPCD) treatment on quality of button mushroom (Agaricus bisporus). Mushrooms were dipped for short time in different HPCD, then stored at 4 ℃ for 8 days (d). Changes in the weight loss, firmness, color, total phenolics, ascorbic acid and activities of polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), and peroxidase (POD) were measured. The results indicated that 0.3 MPa CO₂ maintained a high level of firmness, delayed browning, promoted the accumulation of phenolics, ascorbic acid, inhibited the activities of PPO and POD, and increased PAL activity during the storage period. Thus, 0.3 MPa HPCD treatment has positive effects on improving the quality and colour of button mushrooms.